FWIW during the early 1980’s I purchased a Carver C-4000 preamplifier, which included sonic holography as well as some of the other functions that are provided by your C-16, while selling for a considerably higher price than the C-16 (which I believe was introduced toward the end of that decade).
After a few years I replaced the C-4000 with a Mark Levinson ML-1, which resulted in a truly "night and day" sonic improvement. So after doing a bit of research on your other components I suspect that your preamp is the weakest link.
If after replacing the C-16 you want to retain the sonic holography feature you should be able to find a C-9 at very low cost. The C-9 provides only that function and is used in conjunction with a separate preamp. I didn’t miss that function at all, btw, after I started using the ML-1.
Also, I believe your power amp is nearly 20 years old, and so it might be approaching the point at which significant degradation of the capacitors in its power supply will be occurring, if that has not already started to occur. Its present market value appears at best to be in the vicinity of only $500, so when and if its electrical condition seems to become an issue replacing it with something else, rather than having it overhauled, would seem to be in order.
Good luck. Regards,
-- Al